Cellular telecommunications is one of the fastest growing and most demanding telecommunications applications. Today it represents a large and continuously increasing percentage of all new telephone subscriptions around the world. A standardization group, European Telecommunications Standards Institute (ETSI), was established in 1982 to formulate the specifications for the Global System for Mobile Communication (GSM) digital mobile cellular radio system.
With reference now to FIG. 1 of the drawings, there is illustrated a GSM Public Land Mobile Network (PLMN), such as cellular network 10, which in turn is composed of a plurality of areas 12, each with a Mobile Switching Center (MSC) 14 and a Visitor Location Register (VLR) 16 therein. The MSC/VLR areas 12, in turn, include a plurality of Location Areas (LA) 18, which are defined as that part of a given MSC/VLR area 12 in which a Mobile Station (MS) 20 may move freely without having to send update location information to the MSC/VLR 14/16 that controls the LA 18. Each LA 12 is divided into a number of cells 22. The MS 20 is the physical equipment, e.g., a car phone or other portable phone, used by mobile subscribers to communicate with the cellular network 10, each other, and users outside the subscribed network, both wireline and wireless.
The MSC 14 is in communication with at least one Base Station Controller (BSC) 23, which, in turn, is in contact with at least one Base Transceiver Station (BTS) 24. The BTS 24 is the physical equipment, illustrated for simplicity as a radio tower, that provides radio coverage to the geographical part of the cell 22 for which it is responsible. It should be understood that the BSC 23 may be connected to several BTS's 24, and may be implemented as a stand-alone node or integrated with the MSC 14. In either event, the BSC 23 and BTS 24 components, as a whole, are generally referred to as a Base Station System (BSS) 25.
With further reference to FIG. 1, the PLMN Service Area or cellular network 10 includes a Home Location Register (HLR) 26, which is a database maintaining all subscriber information, e.g., user profiles, current location information, International Mobile Subscriber Identity (IMSI) numbers, and other administrative information. The HLR 26 may be co-located with a given MSC 14, integrated with the MSC 14, or alternatively can service multiple MSCs 14, the latter of which is illustrated in FIG. 1.
The VLR 16 is a database containing information about all of the MS's 20 currently located within the MSC/VLR area 12. If an MS 20 roams into a new MSC/VLR area 12, the VLR 16 connected to that MSC 14 will request data about that MS 20 from the HLR database 26 (simultaneously informing the HLR 26 about the current location of the MS 20). Accordingly, if the user of the MS 20 then wants to make a call, the local VLR 16 will have the requisite identification information without having to reinterrogate the HLR 26. In the aforedescribed manner, the VLR and HLR databases 16 and 26, respectively, contain various subscriber information associated with a given MS 20.
It should be understood that the aforementioned system 10, illustrated in FIG. 1, is a terrestrially-based system. In addition to the terrestrially-based systems, there are a number of satellite systems, which work together with the terrestrially-based systems to provide cellular telecommunications to a wider network of subscribers. This is due to the fact that the high altitude of the satellite makes the satellite visible (from a radio perspective) from a wider area on the earth. The higher the satellite, the larger the area that the satellite can communicate with.
Within a satellite-based network 10, as shown in FIG. 2 of the drawings, a system of satellites 200 (only one of which is shown) in orbit are used to provide communication between MS's 20 and a satellite-adapted Base Station System (SBSS) 220, which is connected to a Mobile Switching Center 14. The MS 20 communicates via one of the satellites 200 using a radio air interface. The satellite 200 in turn communicates with one or more SBSSs 220, which consist of equipment for communicating with the satellites 200 and through the satellites 200 to the MS's 20. The antennae and satellite tracking part of the system is the Radio Frequency Terminal (RFT) subsystem 230, which also provides for the connection of the communication path to the satellite 200.
In such satellite networks 10, a coverage area 205 for a satellite 200 can be (and usually is) very large. This area 205 can be served by a number of MSCs 14 which are connected to Public Switched Telephone Networks (PSTNs) (wireline networks), PLMNs (cellular networks) and each other. As in a normal GSM system, each MSC 14 may serve a number of different SBSS's 220, each of which are associated with a particular set of satellite cells 250. It should be understood that the coverage area for a satellite cell 250 is much larger than the coverage area for a normal GSM cell 22 (shown in FIG. 1). This is due to the fact that a satellite beam 210 directed at a particular satellite cell 250 can cover more area than a signal transmitted from a BTS 24 (shown in FIG. 1) on earth.
The satellite 200 transmits a different beam 210 to each satellite cell 250. When an MS 20 moves from one satellite cell 250 into a new satellite cell 250, the MS 20 detects this change by the presence of a new satellite beam 210 for that new satellite cell 250. This triggers the MS 20 to perform a location update. During the location update process, the current PLMN 10 is displayed to the mobile subscriber on the MS 20. Therefore, the mobile subscriber knows whether the MS 20 has roamed outside of the home network 10.
However, if a mobile subscriber crosses a boundary between two countries, this information may not be transmitted to the mobile subscriber. In many cases, the boundaries between countries are not obvious, and the PLMN 10 that the MS 20 is registered with may span several countries. Having knowledge of these boundaries may help the mobile subscriber in making originating calls as to which dialing plan is applicable. For example, if a subscriber has just unknowingly roamed from Germany to Holland, and he/she dials a number to a German subscriber in national format, the call will be routed to Holland instead. Thus, in such cases, valuable satellite resources are used, but the call is routed incorrectly.
Even if the country information is transmitted to the MS 20 during the location update process, the MS 20 may not perform the location update until after the border has been crossed and the mobile subscriber has traveled several miles into the other country. This delay in performing location updates may be due to a number of factors, such as cell reselection hysteresis and cell movement in the satellite network.
Currently, when an MS 20 within a satellite PLMN 10 originates a call to a dialed B-number, the MS 20 provides Global Positioning System (GPS) coordinate information to the satellite network (MSC 14). The MSC 14 takes this GPS coordinate information and utilizes a database 15 of GPS coordinates and associated country codes to append the country code in front of the B-number. If the MS 20 had a similar type of database within it, the MS 20 may be able to convert received GPS coordinates into the current country and display the current country to the mobile subscriber. However, the database in the MS 20 would have to be limited, because it would not be possible to cover all potential coordinates and associated countries and store this information in a memory that would fit into an MS 20. In addition, the database within the MS 20 may not produce exactly the same country as the network database 15. As an example, if the MS 20 displays Germany and the mobile subscriber attempts to use the German numbering plan to make a call, while the MSC 14 calculates the MS 20 position to be in Holland, this may result in a failed call setup.
It is, therefore, an object of the present invention to provide accurate country information to mobile subscribers within a satellite network.